Scientists Build a More Durable MEMS Switch

Scientists from Binghamton University’s Mechanical Engineering Department have formulated a way to make power lines and cell phones more robust.

Credit: Binghamton University

Assistant Professor Sherry Towfighian and graduate student Mark Pallay developed a new type of microelectromechanical system—more universally known as a MEMS switch—that employs electrostatic levitation to provide a more robust system.

All cell phones use MEMS switches for wireless communication, but traditionally there are just two electrodes. Those switches open and close numerous times during just one hour, but their current lifespan is limited by the two-electrode system.

Sherry Towfighian, Assistant Professor, Mechanical Engineering Department, Binghamton University

When the two electrodes come into contact—after numerous repetitions—the surface of the bottom electrode becomes damaged, resulting in a MEMS switch that has to be cast-off and replaced. Some scientists have tried to prevent the damage by incorporating dimples or landing pads to the electrodes to decrease the contact area when the electrodes make contact, but Towfighian explained that this just delays the ultimate breakdown of the material.

She aimed to develop a system that prevents the damage altogether. Rather than following the two-electrode model, she engineered a MEMS switch having three electrodes on the bottom and one electrode parallel to the others. The two bottom electrodes on the left and right side are charged while the top and middle electrodes are grounded.

“This type of MEMS switch is normally closed, but the side electrodes provide a strong upward force that can overcome the forces between the two middle electrodes and open the switch,” explained Towfighian. This force, known as electrostatic levitation, is presently not available with the two-electrode system. The ability to produce this force stops permanent damage of the device after nonstop use and enables a reliable bi-directional switch.

For cell phones, this design means longer life and fewer component replacements. For power lines, this type of MEMS switch would be useful when voltage goes beyond a limit and we want to open the switch. The design allows us to have more reliable switches to monitor unusual spikes in voltage, like those caused by an earthquake, that can cause danger to public safety.

Sherry Towfighian, Assistant Professor, Mechanical Engineering Department, Binghamton University

The study titled “A reliable MEMS switch using electrostatic levitation” was published in the November 20th issue of the Applied Physics Letters. It was sponsored by the National Science Foundation’s Division of Electrical, Communications and Cyber Systems (ECCS) grant #1608692.

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